You know, the Japanese have this really cool thing with blood types. From what I've been told, they use it like we used the horror scope in other countries to tell about your compatibility with other people. They think that your blood type tells all about you in your personality. It's pretty cool

The downside is that you have to actually know your blood type to use it. Still, it might make an interesting addition to the birthday list without going off topic, because it is Japanese related.